Sensors such as speed or position sensors are used to provide feedback information in mechatronic systems, and are thus used as an interface between the mechanical and the electrical domain. In many cases, the positioning of a sensor is driven by mechanical constraints, for example, the available constructed space or accessibility of sensing targets (target wheel, shaft end, etc.). Therefore, in most applications the sensor cannot be embedded into the electronic control unit (ECU) but can operate as a standalone sensor (satellite sensor) that has to be connected to the control unit through a (wired) interface.
In terms of performance, the sensor interface in many conventional systems provides the “bottleneck” for the information transfer. While the sensing information (e.g., sensing and diagnostic data) is available at a much higher resolution (in time and/or accuracy) at the sensor location, it cannot be transferred and used at that resolution in the ECU because of missing connection bandwidth. Additionally, many conventional interfaces only provide a one-way data link (e.g., sensor to ECU, but not vice versa), thus a dynamic adjustment of sensor parameters or even synchronization between sensor and ECU is not possible, resulting in performance degradation of the entire system. Finally, most conventional connection schemes are point-to-point connections between sensor and ECU. In these situations, complex systems comprising several remote sensors result in complex wiring harnesses.
Automotive systems continue to increase in complexity in order to meet new requirements in terms of emission and safety. These can prevent new challenges with respect to engine and system efficiency. To continue having safe and dependable systems in automotive products, as they increase in complexity while reducing cost, smarter digital sensors are in demand. The Single Edge Nibble Transmission (SENT) digital communication protocol is a promising low-cost solution for communication between sensor satellites and a microcontroller. Short PWM code (SPC) provides application relevant functionalities which are not included in SENT while still keeping as close as possible to the original protocol. However, SPC adds bi-directionality, synchronicity and bus capability. The SPC protocol can aim to extending the SENT communication link in terms of functionality, performance and cost efficiency.
Sensor systems can generally use pin-to-pin interfaces for sensors. Typical implementations are single-ended voltage interfaces (with 3 wires per sensor, such as SENT (single edge nibble transmission), SPC (short PWM (pulse width modulation) code, etc.) or current interfaces (with 2 wires per sensor, such as those used in ABS (anti-lock braking system) or transmission speed sensors). Conventional interface varieties include digital voltage interfaces, analog voltage interfaces, basic current interfaces, and complex current interfaces.
In digital voltage interfaces, SENT is a universal interface used to transfer a digital data stream to the ECU (e.g., unidirectionally) without synchronization and bus capability. SPC can represent an extension of SENT, enabling synchronization and basic bus capability. The implementation of the physical layer interface can be basic, thus the available bandwidth (and therefore the resulting baud rate) of the interface be limited (20 kBaud). Due to the basic implementation, the interface exhibits a high vulnerability when exposed to electromagnetic interference (EMI) or electrostatic discharge (ESD). A strong benefit of SENT/SPC can be the low complexity of the physical layer and the possibility to transfer digital data comprising both sensing and diagnostic data. However, due to the low update rate, it can be insufficient for many applications (e.g. rotor position sensing).